Electron discharge tube



Jan. 13, 1942. H. B. BARTELINK 2,270,159

ELECTRON DISCHARGE TUBE Filed Sept. 9, 19:59

Fig. I.

07 Inventor! Everhard H48. B rtlink,

is Attorney.

Patented Jan. 13, 1942 ELECTRON DISCHARGE TUBE Everhard H. B. Bartelink,- Schenectady, N. Y., as-.

signor to General Electric Company, a corporation of New York Application September 9, 1939, Serial No. 294,168

7 Claims.

This invention relates to electron discharge tubes, and more particularly to light-producing tubes suitable for use in forming a light picture, While not limited to such application, the tubes of my invention are particularly useful in connection with the production of large size luminous displays, Specific examples of such displays include animated signboards and other display surfaces on which it is desired to reproduce on a magnified scale, and by electrical means, a pic-' ture or image of which the original exists at a more or less remote control station.

In applications of the type referred to it is impractical to project a light picture of the order of 100 feet square and the only practical method to obtain sufficient light intensity in the picture appears to be to use a number of individual lamps to form the picture elements. If a 200 line picture is required, there must be 40,000 lamps used to form the image screen. If, however, a colored display is wanted, this large number of lamps must be increased at least three times, or to 120,000 lamps. Furthermore, each lamp must be provided with its individual terminals and mountings so that the cumulated cost of the whole signboard becomes very great. It is a primary object of my present invention to provide tube constructions by which this cost may be very much reduced without in any way lessening the flexibility of the reproducing system as a whole.

In the attainment of this object an important feature of my invention consists in the provision of a fluorescent tube with several sections, each of which produces light in response to a separate control impulse, and in which a common cathode and common anode are used for all the sections. By such use of a single cathode and single anode for several separate electron discharge streams, a large reduction in the total number of tubes and in the mounting accessories required for a given display capacity is made possible.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 is a front view, partly in section, of one embodiment of my invention; Fig. 2 is a side or end sectional view of the apparatus illustrated in Fig. 1; Fig. 3 is a detailed perspective view of certain parts of the apparatus illustrated by Fig. 1; Fig. 4 is a circuit diagram illustrating schematically a circuit connected with apparatus such as that of Fig. 1; Fig. 5 is a side View, partly in section, of a somewhat difierent em bodiment of my invention; Fig. 6 is a front sectional view of the apparatus illustrated by Fig. 5; and Fig. 7 is a detailed perspective view of certain parts of the apparatus illustrated by Fig. 5. 7

Referring to Fig.1, there is shown a fluorescent tube constructed in accordance with my invention, in which three separate sections, having a common means for producing separate electron discharge streams therein, are enclosed with a common evacuated envelope It. This common means includes an elongated semi-cylindrical anode II positioned near the wall of the envelope I0 and a long indirectly heated cathode I2, axially placed with respect to the anode II. A pair of mica barriers I3 and I4 are placed perpendicularly to the cathode so as to divide the space between the cathode and the anode into three separate sections. The form of these mica barriers I3 and I4 and their cooperation with the anode I I is explained at greater length hereinafter.

The anode II is indicated in Fig. 2 as having a slot 25 formed therein through which a projecting portion I5 of the mica barrier I4 extends. This portion I5 aids in maintaining the barrier I4 in its proper position in supporting relation to the various elements in the envelope I0. The mica barrier I3 is of the same shape as the barrier l4 and is placed within the envelope I0 to act as a support for the parts and a division between the adjacent electron streams in exactly the same way as the barrier I4. Holes are provided centrally ofthe mica barriers I3 and M through which the cathode I2 passes. Each portion of the surface of the anode II, which corresponds to one of the three separate sections formed by the mica barriers, is coated with a different type of fluorescent material. The three types are chosen to provide three complementary colors (upon bombardment by an electron stream). The configuration of the anodell and the cathode I2 is such as to produce an electron discharge therebetween, on' the application of a voltage on the anode positive with respect to the cathode, which discharge impinges uniformly upon the entire luminescent area of the surface of the anode.

To regulate the intensity of this electron discharge and thereby control the amount of light produced in each respective section of the tube, suitable grids or control electrodes I6, I! and I8 are provided for the respective electron streams in the three separate sections of the fluorescent tube. These control electrodes are represented as helical wires arranged axially with respect to the common cathode I2, A hole I9 is formed in the mica barrier I4 to allow passage therethrough of the conductor leading to the control electrode I8. A hole in the mica barrier I3 and another hole (not shown) corresponding to the hole I9 allow passage therethrough of the conductors connected respectively to the control electrodes I1 and I8. It is preferred that these conductors be placed outside the direct path between the common cathode I2 and the common anod II, in order to prevent the formation of shadows on the fluorescent screens. A common accelerating or screen grid 2I for the three separate sections is shown as being formed of three interconnected helical coils. A hole 22 in the mica barrier I4 allows passage therethrough of a conductor which connects together the two coils in the sections on opposite sides of the barrier I4. A similar hole 23 in the barrier I3 allows passage therethrough of a conductor which conducts together the two coils on the opposite sides of the barrier I3.

For supporting the tube as a whole, and for providing electrical connections to the electrical elements therein, there is provided a base or plug 24 fastened to one end of the container I ll. Seven pin terminals of usual construction are formed in the base 24 and are connected respectively: to the unipotential cathode surface I2, to one end of the cathode heater, to the control grid I6, to the control grid I1, to the control grid I8, to the screen grid 2|, and to the anode II. It is clear that if the tube were constructed with three separate evacuated containers, one for each color, separate terminals would be necessary on each of the three corresponding bases for: the cathode surface, the cathode heater, the screen grid, and the anode, as well as one for the control grid. For each tube, therefore, five terminals would be necessary and the total number of terminals necessary for the three tubes to replace the one tube of my invention would be fifteen, whereas the simplified single tube has only seven terminals.

In order to show more clearly the cooperation between the mica barrier and the common anode II, they are illustrated in Fig. 3 in disassembled relation. The proper assembly of these parts is made apparent by this view in which it clearly appears that the projecting portion l5 of the barrier I4 is adapted to extend through the slot 25 in the anode II. The edge of the barrier I4 adjacent the anode I I is shaped to fit snugly thereagainst and the remaining edge portion of the barrier I4 is shaped to bear against the part of the wall of the envelope II] which is not covered by the anode II. The barrier I4 thus provides a convenient and easily formed support for the anode II and for the grids to maintain their positions fixed in the envelope Ill. The barrier I3, as was explained previously, is similarly shaped and cooperates with the various parts in the same way.

In Fig. 4 there is shown a simple circuit which may be provided for the operation of the tube shown in Fig. 1. The tube is represented schematically; the common anode, cathode, screen grid, and control electrodes being given the same reference numerals as in Fig. 1. A transformer 26 is connected on one side of its secondary to the cathode heater and on the other side of its nected from the cathode I2 through a load resistor 39 to the anode I I. The electron discharge maintained by this potential on the anode II is accelerated toward the anode II by a positive potential on the screen grid 2|. The potential on the grid 2| is produced in the apparatus shown by connecting the grid 2| to a suitable point of the source 21 of operating potential. The potential of the screen grid may be more or less positive than the anode, and as illustrated it is less positive.

The several electron discharge streams induced between the anode I I and the cathode I2 by the source 2! of operating potential are controlled by the individual control grids I6, I1 and I8, which are connected to suitable means for applying such potentials to the grids as to allow production of light elements at appropriate times and places on the display surface to form a desired picture. It is unnecessary to describe completely such suitable means since they form no part of the present invention, and since they are well known, as, for example, the apparatus described and illustrated by Frank Gray, J. W. Horton, and R. C. Mathes in the Bell System Technical Journal for October, 1927, on pages 5'70 to 573. This apparatus utilizes a scanning disk mechanism for creating signal impulses corresponding to successive light and dark areas of the object whose picture is to be transmitted, and a distributor or commutator for transferring these impulses synchronously to corresponding light-forming elements in a large bank of glow tubes, which constitutes the display surface. Such apparatus, if used to produce three-color images, requires three scanning means and three distributors for rapidly switching the incoming signal impulses from one picture element to another.

In the present connection it will be assumed that signal impulses developed in some such manner as that specified in the foregoing paragraph are being periodically applied to the terminals 90, 9| and 92 of the apparatus shown in Fig. 4, or more properly between such terminals and the common or ground terminal 28. In order to provide a practical means for transmitting the signal impulses from the terminals 90, 9|, and 92 to the grids I6, I], and I8, of the light-producing tube, I may make use of a series of amplifiers arranged as shown at 32, 33, and 34. These amplifiers are utilized in the following manner:

The potentials applied to the grids IS, IT, and I B are made directly responsive to the current flow through the various amplifiers by means of resistors 29, 30 and 3| placed in series with the amplifiers and respectively connected between the cathode I2 of the light-producing tube and its various grids. With this arrangement it is apparent that the voltage impressed on any particular grid of the light-producing tube is determined directly by the voltage drop across its associated resistance, such drop being in turn responsive to the current now through the amplifier which is serially connected with the resistance in question. The current flow through each amplifier is made responsive to the signal impulses applied to a corresponding one of the input terminals 90, 9|, and 92 by connecting such terminal directly to the grid of th amplifier.

It is desired that the discharge in any given section of the light-producing tube as determined by the potential applied to its associated grid shall be not merely an instantaneous discharge but shall be of such character as to maintain the lamp section in question luminous during substantially the total period between the receipt of successive signal impulses. To this end a condenser is provided in series with each of the amplifier grids, such condensers being shown at 36, 31, and 38 as being connected between the common terminal'line 28 and the various grids. By virtue of the presence of these condensers the potential which is attained by any individual grid as the result of the application of a signal impulse to such grid is maintained for an appreciable interval of time by the charge retained on the associated condenser. Consequently, current fiow through the amplifier with which the grid is associated is sustained at a fairly even value during the interval between successive signal impulses. This value, of course, is changed upon the receipt of a new signal impulse and in accordance with the strength of such impulse so that the brightness of the light emitted by each section of the light-producing tube is enabled to vary cyclically in general accord with the brightness of the primary image from which the signal impulses are derived. The

frequency of brightness-change consequently need not be very high, as it would have to be if the discharge in each section of the lightproducing tub were substantially instantaneous, but may, for example, be of the order of changes per second. It is thus possible, in a display surface utilizing a large number of lightproducing tubes, to obtain animated effects simulating the action of moving pictures, without using a very high frequency of brightness change.

Referring to Fig. 5, a somewhat different form of tube is shown, which is adapted to emit light in the direction away from the base rather than in a direction perpendicular thereto, as in the tube shown in Fig. 1. An evacuated envelope 4!] of conical shape, having a fiat or convex front face, contains an anode 4| which is V-shaped, with a flat central or base portion. Fluorescent material coated upon the sides of the anode 4| toward the front face of the envelope 40 is in a position to emit light through the front face of the envelope when the material is properly excited.

As is more clearly shown in Fig. 6, three cylindrical cathode surfaces 42, 43, and 44 are arranged to furnish electron streams to excite such fluorescent material and lie parallel to each other and perpendicular to the flat central portion of the anode 4|. Suitable openings are cut through the fiat central portion of th anode for passage therethrough of the cathode surfaces and their accompanying connections. These three cathode surfaces are solidly interconnected, in a manner not shown, to form a common cathode for three separate compartments corresponding to the three separate light colors to be produced. The space within the envelope 4|! is divided into these three compartments by mica barriers 45 and 46 which extend across the space within the envelope and lie betweenthe several portions 42,

43 and 44 of the cathode. Each compartment contains a portion of the common cathode formed by the three cathode surfaces, and a corresponding portion of the common anode 4|. There is produced in each compartment an electron discharge stream between these corresponding portions of the cathode and anode, which impinges substantially uniformly on the fluorescent coating on the anode. This discharge is produced by application of suitable operating potential between the anode and the cathode.

In order to control the separate electron discharge stream in each compartment, three control grids 41, 48, and 49 are provided, each of these control grids comprising a helical coil of wire arranged axially around its corresponding portion of the common cathode. In this form of fluorescent tub no screen or accelerating grid is shown, as it may be unnecessary to provide one in certain cases.

Without a screen grid there are six connections necessary to this tube to control the three spots of light which can be produced thereby. A base or plug 50 (shown in Fig, 5) is provided with six pin terminals of usual construction which are connected to the elements of the tube as follows: to the cathode comprising the surfaces42, 43, and 44; to the cathode heaters for the three surfaces; to the anode 4|; to the control grid 41; to the control grid 48; and to the control grid 49.

The construction and inter-relation of the mica barrier and the anode 4| of the tube shown in Figures 4 and 6 is illustrated more clearly in the detailed perspective View of Fig. "I. As shown therein, the anode 4| is provided with a pair of parallel slots 5| and 52 extending across the flat central portion of the anode so that there remains only a small portion of the anode near the edges of its divergent sides. The mica barrier 45 is adapted to slide within the slot 5| and is provided with notches 53 and 54, which are so placed as to encompass the small edge portions of the anode 4| which are leftby the slot 5|. The inter-fitting of the anode and the mica barriers provides a convenient support for the anode, since the barriers fit snugly against the envelope 4!]. The holes 55, 56 and 51 formed in the flat central portion of the anode 4|, for the passage therethrough of the three cathode surfaces and the corresponding control grids, are shown in detail. The mechanical interrelation of the mica barriers and the common anode is thus made apparent, so that it may be easily understood how the three separate electron streams are formed between the respective sections of the common cathode and the common anode.

The fluorescent tube shown in Figs. 5 and 6 is intended to operate in substantially the same way as the tube shown in Figs. 1 and 2, and may be connected in a substantially identical circuit. As pictured in Fig. 6 the tube has one advantage over the tube shown in Fig. l for the purpose of forming a three-color picture. It is apparent that the common anode 4| which forms one picture element having three differently colored parts. is approximately square and therefore appearses a single spot of light at a little distance. even though the portions of the anode 4| which form the three colors are slightly separated. The tube illustrated in Fig. 1 is some what better adapted to forming three individual picture elements in a picture formed of a single color. To adapt it for three-color pictures the semi-cylindrical anode II should be shorter in the direction of its axis and should have a diameter substantially equal to its length. It is obvious how such a change in dimension may be made.

It is, of cause, obvious that many more sections may be provided in either of the particular tubes illustrated herewith. For example, twelve separate sections may easily be provided in a very long tube of the type shown by Fig. 1, in which every third section produces the same color of light in response to separate control impulses. By such use of a large number of sections in a single tube, it is possible to make an even larger reduction in the number of terminals for a particular display surface and a corresponding reduction in the expense for assembling the apparatus for operation.

In most of the fluorescent lamps in a large picture-forming apparatus the resistor 39 may not be desirable since it may lower the efiiciency slightly. However, since the voltages impressed on the three control electrodes, as in the circuit of Fig. 4, are mixed in the tube shown, just as in a mixer or converter tube, the voltage across the resistor 39 is a measure of these intermixed control voltages and therefore is also a measure of the total brightness of the tube. This convenient measure of brightness may be used to adjust the screen for brilliant operation in the day or at dusk and for less bright operation in the darkness of night.

While I have shown particular embodiments of my invention, it will, of course, be understood that I do not wish to be limited thereto since different modifications may be made both in the circuit arrangement and instrumentalities employed, and I aim by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. The combination, in a lamp having a surface which bears a coating of fluorescent material whose area is of the order of magnitude of the cross-sectional area of said lamp, of means operative during normal use of said lamp to produce a diffuse electron discharge which continuously impinges substantially uniformly on said coating over its entire surface, means for dividing said electron discharge into a plurality of separate streams, each of said streams being directed to an individual portion of said coating and thereby causing light emission from each portion over its entire surface, and separate means cooperating with each of said streams for controlling its intensity in response to individual control impulses without substantially affecting the uniform diffusion of said discharge, said separate means being thereby effective to control the light emission from each of said individual portions in accordance with said control impulses.

2. The combination, in a multicolor lamp having a supporting surface, and means operating normally to produce a diffuse electron discharge impinging on said surface, of means for dividing said electron discharge into a plurality of separate streams, each of said streams continuously impinging on an individual portion of said surface with substantially uniform intensity over the entire area of said portion, a fluorescent coating on-each of said portions, each of said coatings being adapted to produce light of distinctive color upon electron bombardment, the total area of said coatings being of the order of magnitude of the cross-sectional area of said lamp, and

means controllable in accordance with a signal impulse for separately adjusting the intensity of each stream without affecting the uniform diffusion of said stream, thereby independently to control the intensity of light emitted by the coating associated with such stream without affecting the uniform emission of such light over the entire area of each portion of said surface.

3. In combination with a plurality of fluorescent screens, each of said screens being adapted to produce a distinctive color of light upon electron bombardment and each being of appreciable area, common means associated with said screens operating normally to direct a plurality of diffuse electron discharge streams thereagainst, each of said streams being of a cross section approximately equal to the area of the corresponding fluorescent screen and impinging continuously with substantially uniform intensity over the entire surface thereof, thereby causing light emission from each screen substantially uniformly over its entire surface area, and a plurality of control electrodes, the total area of said fluorescent screens being of the order of magnitude of the cross-sectional area of the structure formed by said screens, said common means, and said control electrodes, each of said electrodes being arranged to respond to a respective signal voltage impressed thereon and to adjust accordingly the intensity of a corresponding stream without substantially affecting the uniform diffusion of each such stream over the corresponding one of said screens, whereby the intensity of colored light emitted from each of said screens is a function of the corresponding signal voltage.

4. A lamp comprising an evacuated container having a terminal and mounting base affixed to one end thereof, an anode in said container having a plurality of fluorescent electron-receiving surfaces, the combined area of said fluorescent surfaces viewed from a point outside said container being substantially coextensive with the viewed area of said container, means operative normally to cause a diffuse electron stream to impinge continuously against each of said fluorescent surfaces with substantially uniform intensity over its entire area, thereby producing light with substantially uniform intensity over such area, said means comprising an equipotential cathode structure having a plurality of emitting parts corresponding in number to said fluorescent surfaces, a plurality of control electrodes respectively associated with the various cathode parts, each of said electrodes being arranged to respond to a respective signal voltage impressed thereon and to adjust accordingly the intensity of a corresponding stream without substantially affecting the uniform diffusion of each such stream over the corresponding one of said fluorescent surfaces, whereby the fluorescence of each of said screens is controlled in response to a corresponding signal voltage, and lead-in connections for said anode, cathode, and control electrodes provided through said mounting base.

5. A lamp having a plurality of fluorescent screens in an elongated evacuated container with a mounting base at one end, said screens being substantially coextensive in area with the walls of said container when viewed from a point at one side of said lamp, means in said container operative normally to cause an independent diffuse electron stream to impinge continuously with substantially uniform intensity over the entire surface of each of said screens to cause fluorescence thereof, said means comprising a single cathode running longitudinally of said container and a single anode having separate portions of its surface carrying said screens and arranged parallel to said cathode, and a plurality of control electrodes adjacent said cathode, one of said electrodes being arranged to control each of said independent electron streams in accordance with an individual control voltage impressed on said electrode without substantially affecting the uniform diffusion of said streams, whereby lo the fluorescence of each of said screens is adjusted in accordance with a corresponding control voltage.

6. A lamp comprising an evacuatedcontainer, a screen of fluorescent material therein Whose area viewed from a point outside said container is substantially co-extensive with the viewed area of said container, means in said container operative normally to project a diffuse electron discharge which continuously impinges substantially uniformly on said screen over its entire surface, thereby producing light substantially uniformly over such surface, and means for separately controlling the intensity of Various portions of said discharge without substantially aifecting the uniform diffusion of each such portion of said discharge over the corresponding surface portion of said screen in order to control the electron currents respectively impinging on individual portions of said screen and the resulting light in accordance with corresponding control voltages.

7. A lamp comprising an evacuated container having a light transmitting wall portion, a target of fluorescent material in said container positioned to be viewed through said light transmitting Wall portion, means in said container operative normally to project a, plurality of separate diffuse electron streams toward said target, each of which impinges continuously on an individual portion thereof with substantially uniform intensity over its entire surface, the total area of such portions of said target being of the order of magnitude of the cross-sectional area of said lamp, thereby producing light substantially uniformly over such surface, and means for separately controlling the intensity of light emitted by each portion of said target in accordance with a corresponding control voltage, said last means acting to adjust the intensity of each of said streams without substantially affecting the uniform diffusion of each such stream over the corresponding surface portion of said target in order-t0 control the electron current respectively impinging on individual portions of said target with a corresponding control of the intensity of light emitted therefrom.

EVERHARD H. B. BARTELINK. 

